Advisory of Transportation U.S. Department Circular Federal Aviation Administration Subject: VISUAL INSPECTION FOR Date 8/14/97 AC No: 43-204 AIRCRAFT Initiated by: AFS-350 Change:
1. PURPOSE. This advisory circular (AC) provides technical information to persons conducting a visual inspection of aircraft.
The procedures presented in this AC are an acceptable means, but not the only acceptable means, for conducting visual inspections and inspection programs. Where the aircraft, engine, propeller, or appliance manufacturer has published a recommended inspection schedule or program for a particular aircraft, that program should take precedence over the recommendations of this AC.
2. RELATED READING MATERIAL.
a. AC 20-37D, Aircraft Metal Propeller Maintenance.
b. AC 43-3, Nondestructive Testing in Aircraft.
c. AC 43-4A, Corrosion Control for Aircraft.
d. AC 43-7, Ultrasonic Testing for Aircraft.
e. AC 43-12A, Preventive Maintenance.
AC 43.13-1A, Acceptable Methods, Techniques and Practices--Aircraft Inspection and Repair.
Richard O. Gordon Acting Deputy Director, Flight Standards Service
For sale by the U.S. Government Printing Office Superintendent of Documents, Mail Stop: SSOP, Washington, DC 20402-9328 ISBN 0-16-050415-5
CONIENTS Paragraph Page No.
CHAPTER 1. GENERAL
1. INTRODUCTION.
2. RELATION OF VISUAL INSPECTION TO NONDESTRUCTIVE INSPECTION.
3. DEFINITION OF VISUAL INSPECTION.
4. PURPOSE OF VISUAL INSPECTION.
5. AIRFRAME AND ENGINE STRUCTURAL DETAILS.
6. FACTORS AFFECTING VISUAL INSPECTION.
7. SAFETY.
8. THE VISUAL INSPECTION PROCESS. 19
9. VISUAL INSPECTION, GENERAL. 20
10. AIRFRAME VISUAL INSPECTION. 21
11. ENGINE VISUAL INSPECTION. 24
12. INSPECTION FOR SPECIFIC TYPES OF CORROSION.
13.-199. RESERVED. 31 CHAPTER 2. VISUAL INSPECTION PROCEDURES
200. GENERAL.
201. MATERIAL CONTAINED IN A VISUAL INSPECTION PROCEDURE. 43
202. ACTIVITIES APPLYING TO ALL VISUAL INSPECTIONS.
203. RECORD KEEPING. 45
204. FOUR LEVELS OF VISUAL INSPECTION. 47
205. ACCEPTABLE PRACTICE FOR VISUAL INSPECTION. 47
206.-299. RESERVED. 52 CHAPTER 3. VISUAL INSPECTION AIDS 63
300. GENERAL. 63
301. LIGHTING AND ILLUMINATION. 63
302. LIGHTING SYSTEMS. 100
303.-399. RESERVED. 104 CHAPTER 4. EQUIPMENT USED IN VISUAL INSPECTION 117
400. GENERAL. 117
401. MAGNIFYING DEVICES. 120
402. PHOTOGRAPHIC AND VIDEO SYSTEMS. 120
403. OPTICAL COMPARATORS. 126
404. BORESCOPES. 127
405. LIST OF EQUIPMENT USED IN VISUAL INSPECTION. 156
406.-499. RESERVED. 156 CHAPTER 5. DEFINITIONS 167
500. DEFINITIONS. 167
501.-599. RESERVED. 173 Page i
APPENDIX A. BEACHCRAFT, ATA CODE 57-10, SAMPLE INSPECTION
PROCEDURE APPENDIX B. BEACHCRAFT, ATA CODE 55-30, SAMPLE INSPECTION
PROCEDURE APPENDIX C. PRATT & WHITNEY, ENGINE GENERAL--INSPECTION/CHECK- -00, SAMPLE INSPECTION PROCEDURE APPENDIX D. PRATT & WHITNEY, ENGINE GENERAL--INSPECTION/CHECK- -01A, SAMPLE INSPECTION PROCEDURE APPENDIX E. DC-9 SERVICE BULLETIN, SAMPLE INSPECTION PROCEDURE APPENDIX F. BOEING 747 SERVICE BULLETIN, SAMPLE INSPECTION
PROCEDURE APPENDIX G. VISUAL INSPECTION EQUIPMENT APPENDIX H. ENGINE VISUAL INSPECTION GLOSSARY
LIST OF ILLUSTRATIONS Page No.
FIGURE 1-1. AREAS MOST SUSCEPTIBLE TO CRACKS FIGURE 1-2. TYPICAL SURFACE CRACKS FIGURE 1-3. MULTIPLE-SITE DAMAGE SURFACE FATIGUE CRACKS FIGURE 1-4. EXAMPLE OF SKIN-CRACKING AT FASTENERS FIGURE 1-5. AREAS MOST SUSCEPTIBLE TO CORROSION FIGURE 1-6. EXAMPLE OF MISSING RIVET HEADS RESULTING FROM CORROSION PRODUCTS 5 FIGURE 1-7. EXAMPLE OF BLISTERING OF SEALANT IN A FUEL CELL
CAUSED BY CORROSION FIGURE 1-8. EXAMPLE OF CHIPPED AND LOOSE PAINT ON A WING SKIN
CAUSED BY CORROSION FIGURE 1-9. INTERNAL CORROSION OF THE TUBULAR ENGINE MOUNT OF A 1946 VINTAGE CESSNA 7 FIGURE 1-10. CORROSION OF THE RUDDER CONTROL CABLE OF A 1969 CESSNA 172, FOUND VISUALLY 8 FIGURE 1-11. CORROSION OF THE ELEVATOR RIB OF A 1969 CESSNA 172, FOUND VISUALLY 9 FIGURE 1-12. EXAMPLE OF SKIN-BULGING DUE TO CORROSION 9 FIGURE 1-13. EXAMPLE OF CRACKED NUT DUE TO CORROSION 10 FIGURE 1-14. LANDING GEAR AND WHEEL CORROSION POINTS 11 FIGURE 1-15. AREAS MOST SUSCEPTIBLE TO DISBONDING 1 2 FIGURE 1-16. COMMON PHYSICAL CHARACTERISTICS OF ENGINE DEFECTS (3 SHEETS) 13 FIGURE 1-17. TYPICAL DEFECTS AS SEEN THROUGH BORESCOPE AND OTHER AIDS 15 FIGURE 1-18. USING A FLASHLIGHT TO INSPECT FOR SURFACE CRACKS 22 Page ii
FIGURE 1-19. UNIFORM ETCH CORROSION 26 FIGURE 1-20. PITTING CORROSION 27 FIGURE 1-21. GALVANIC CORROSION OF MAGNESIUM ADJACENT TO STEEL FASTENER 28 FIGURE 1-22. CONCENTRATION CELL CORROSION 29 FIGURE 1-23. INTERGRANULAR CRACKING AND CORROSION ON A WINGSPAR CHORD 30 FIGURE 1-24. SEVERE EXFOLIATION CORROSION 31 FIGURE 3-1. EXAMPLE OF THE EFFECT OF SHINY AND MATTE
FINISH OF PARTS AND LIGHTING SYSTEM ORIENTATION ON SEEING TASKS 68 FIGURE 3-2. EXAMPLE OF THE EFFECT OF LIGHTING SYSTEMS ON INSPECTION OF A CIRCUIT BOARD 69 FIGURE 3-3. EXAMPLE OF THE EFFECT OF LIGHTING SYSTEM ORIENTATION ON AN INSPECTION SURFACE 70 FIGURE 3-4. EXAMPLES OF DIRECT AND REFLECTED GLARE 75 FIGURE 3-5. EXAMPLE OF LUMINAIRE SHIELDING ANGLE 77 FIGURE 3-6. HARSH SHADOWS PRODUCED BY UNIDIRECTIONAL
ILLUMINATION (LEFT) AND SOFT SHADOWS PRODUCED BY DIFFUSE ILLUMINATION 79 FIGURE 3-7. MULTIPLE SHADOWS (UPPER LEFT) ARE CONFUSING;
SINGLE SHADOWS (CENTER) MAY CONFUSE, BUT CAN HELP; DIFFUSED LIGHT (LOWER RIGHT) ERASES THE 80 FIGURE 3-8. CORRELATED COLOR TEMPERATURE IN KELVINS OF SEVERAL ELECTRIC LIGHT AND DAYLIGHT SOURCES 82 FIGURE 3-9. INTERNATIONAL COMMISSION ON ILLUMINATION LUMINAIRE CLASSIFICATIONS FOR GENERAL LIGHTING 83 FIGURE 3-10. TYPICAL LAMP AND FIXTURE LIGHT DISTRIBUTION CURVES 84 FIGURE 3-11. ILLUSTRATION OF THE IMPORTANCE OF A WHITE
CEILING FOR IMPROVING THE VISUAL ENVIRONMENT OF AN INDUSTRIAL FACILITY 85 FIGURE 3-12. EXAMPLES OF PLACEMENT OF SUPPLEMENTARY LUMINAIRES 87 FIGURE 4-1. TYPICAL 35MM CAMERA AND CAMERA ADAPTER INSTALLATION ON A RIGID BORESCOPE 121 FIGURE 4-2. TYPICAL BORESCOPE VIDEO ADAPTER SYSTEM 122 FIGURE 4-3. BLOCK DIAGRAM OF A TYPICAL VIDEO INSPECTION SYSTEM 123 FIGURE 4-4. SCOPEMAN HAND-HELD VIDEO MICROSCOPE IMAGING SYSTEM 124 FIGURE 4-5. SMARTSCOPE VIDEO MEASURING MICROSCOPE SYSTEM 125 FIGURE 4-6. SCHEMATIC OF AN OPTICAL COMPARATOR 126 FIGURE 4-7. 127 FIGURE 4-8. THREE TYPICAL DESIGNS OF BORESCOPES 128 FIGURE 4-9. TYPICAL DIRECTIONS AND FIELD OF VIEW OF RIGID BORESCOPES 129 FIGURE 4-10. TYPICAL MICRO-BORESCOPE 133 FIGURE 4-11. TYPICAL EXTENDIBLE BORESCOPE 134 FIGURE 4-12. TYPICAL SCANNING BORESCOPE 135 FIGURE 4-13. ZOOM-A-BORE INSPECTION INSTRUMENT WITH MAGNIFICATION BOOSTER ATTACHED 136 Page iii
FIGURE 4-14. MICRO-BORE VIEWING SYSTEM 137 FIGURE 4-15. MIRROR TUBE VIEWING SYSTEM 139 FIGURE 4-16. DEEP-HOLE MIRROR VIEWING SYSTEM 140 FIGURE 4-17. TYPICAL FLAWS SEEN THROUGH A FLEXIBLE FIBERSCOPE 141 FIGURE 4-18. COMPARISON VIEWS WITH DIFFERENT QUANTITIES OF FIBERS IN THE FIBERSCOPE IMAGE BUNDLE 143 FIGURE 4-19. FLEXIBLE VIDEOSCOPE IMAGES 144 FIGURE 4-20. TYPICAL CCD VIDEOSCOPE RESOLUTION 145 FIGURE 4-21. COMPARISON BETWEEN VIDEOSCOPE AND FIBERSCOPE IMAGES 146 FIGURE 4-22. VIEW THROUGH A MEASURING FIBERSCOPE 147 FIGURE 4-23. RETRIEVAL DEVICE IN BORESCOPE WORKING CHANNEL 148 FIGURE 4-24. FLYING PROBE FLEXIBLE BORESCOPE 151 FIGURE 4-25. VIDEOHOOK PROBE ATTACHMENT FOR A FLEXIBLE BORESCOPE 152 FIGURE 4-26. POWER BLENDING BORESCOPE KIT 153 FIGURE 4-27. SHADOWPROBE™ MEASURING SYSTEM 154
LIST OF TABLES Page No.
TABLE 1-1. ILLUMINANCE LEVELS FOR SAFETY* 18 TABLE 2-1. TOPICS TO BE CONSIDERED IN PREPARING OR REVIEWING
A VISUAL INSPECTION PROCEDURE TABLE 3-1. ILLUMINANCE VALUES 65 TABLE 3-2. WEIGHTING FACTORS TO BE CONSIDERED IN SELECTING
SPECIFIC ILLUMINANCE WITHIN RANGES OF VALUES FOR EACH ILLUMINANCE CATEGORY 66 TABLE 3-3. IES RECOMMENDED ILLUMINANCE CATEGORIES FOR THE
DESIGN AND EVALUATION OF LIGHTING SYSTEMS FOR INDUSTRIAL INSPECTION AREAS 67 TABLE 3-4. CLASSIFICATION OF VISUAL TASKS AND SUPPLEMENTARY LIGHTING TECHNIQUES (3 SHEETS) 71 TABLE 3-5. RECOMMENDED REFLECTANCE VALUES FOR INDUSTRIAL
LIGHTING TABLE 3-6. RECOMMENDED MAXIMUM LUMINANCE RATIOS FOR
INDUSTRIAL LIGHTING TABLE 3-7. TYPICAL PORTABLE LUMINAIRES FOR SUPPLEMENTARY LIGHTING (7 SHEETS) TABLE 3-8. TYPICAL INSPECTION FLASHLIGHTS (5 SHEETS) TABLE 4-1. TYPICAL INSPECTION MIRRORS TABLE 4-2. TYPICAL SIMPLE MAGNIFIERS TABLE 4-3. TYPICAL WORKING CHANNEL DEVICES Page iv
CHAPTER 1. GENERAL INTRODUCTION. Over 80 percent of the inspections on large transport category aircraft are visual inspections. On small transport aircraft the ratio is even greater and on general aviation aircraft, virtually all inspection is visual. Visual inspection is usually the most economical and fastest way to obtain an early assessment of the condition of an aircraft and its components. Most of the defects found on aircraft are found by visual inspections, and the airframe manufacturers and users depend on regular visual inspections to ensure the continued airworthiness of their aircraft. Consequently, it is important that visual inspection methods be understood and properly applied by those responsible for the continued airworthiness of aircraft.
Proficiency in visual inspection is crucial to the safe operatior fairy earning her then eve eden one experiend bument describes those methods and the way they are used in the various inspections carried out on aircraft.
2. RELATION OF VISUAL INSPECTION TO NONDESTRUCTIVE INSPECTION (NDI).
Visual inspection is an essential part of airplane maintenance.
The visual inspection component of NDI requires trained and experienced inspection personnel, using validated procedures and appropriate calibration standards with effective, well-maintained equipment in a well-managed maintenance environment.
3. DEFINITION OF VISUAL INSPECTION. Visual inspection is defined as the process of using the eye, alone or in conjunction with various aids, as the sensing mechanism from which judgments may be made about the condition oi a unit to be inspected. imaging devices are playing an increasing part in the inspection process, (e.g., ultrasonic C-scans, eddy current imaging, realtime X ray). Analysis of such displays is not considered visual inspection and will be covered under image analysis in AC 43-X, Nondestructive Inspection For Aircrait.
1 Goranson, U.F. and Rogers, J.I., 'Elements of Damage Tolerance Verification," 12th Symposium of International Commercial Aeronautical Fatigue, Touluse, France, May 1983.
Chap 1 Par 1 Page 1
4. PURPOSE OF VISUAL INSPECTION.
Visual inspection is used to:
• Provide an overall assessment of the condition of a structure, component, or system.
• Provide early detection of defects before they reach critical size.
• Detect errors in the manufacturing process.
• Obtain more information about the condition of a component showing evidence of a defect.
In many situations, no reliable alternative exists to visual inspection. Visual procedures are mandated by the FAA for structural inspections to support Supplementary Structural Inspection Documents (SSIDs), Service Bulletins (SBs), and Airworthiness Directives (ADS).
5. AIRFRAME AND ENGINE STRUCTURAL DETAILS.
a. Typical Airframe Defects. Typical airframe defects found in aircraft which can be detected by visual inspection can be divided into three types: cracks, corrosion, and disbonding. Other defects, such as system and component wear, accidental damage, environmental damage from long term storage, sunlight, etc., can also be detected visually.
(1) Cracks. Figure 1-1 illustrates areas most susceptible to cracks. Figure 1-2 shows typical surface cracks which can be detected by visual inspection. Surface cracks caused by fatigue are illustrated in Figure 1-3. An example of skincracking at fasteners is shown in Figure 1-4. Sometimes an underlying crack can cause a distortion which can be detected visu- Chap 1 Page 2 Par 4
Empennage General Condition:
Attach Points Engine Mount Attach Points Skin Doublers and Pressure Bulkheads On Pressurized Aircraft Landing Gear Fuel Tanks Wheel Rims Wing Spars and Caps Lower Wing Skins FIGURE 1-1. AREAS MOST SUSCEPTIBLE TO CRACKS Crack - Fastener removed FIGURE 1-2. TYPICAL SURFACE CRACKS Chap 1 Par 5 Page 3
EXTERML 3198
- STA.
58.159 FIGURE 1-3. MULTIPLE-SITE DAMAGE SURFACE FATIGUE CRACKS FIGURE 1-4. EXAMPLE OF SKIN-CRACKING AT FASTENERS
(2) Corrosion. Figure 1-5 illustrates areas most susceptible to corrosion. The various manifestations of corrosion such as missing rivet heads are shown in Figure 1-6.
Chap 1 Page 4 Par 5
Passenger Floor Supports Cargo and and Flooring Crew Doors Galley Areas Under De-Icer Boots Areas in Path of Battery Exhaust Gasses Areas Lavatory Areas Undercarriage Bays Integral Fuel Tanks FIGURE 1-5. AREAS MOST SUSCEPTIBLE TO CORROSION FIGURE 1-6. EXAMPLE OF MISSING RIVET HEADS RESULTING
FROM CORROSION PRODUCTS An example of blistering of paint in a fuel cell caused by corrosion is illustrated in Figure 1-7. Chipped and loose paint on a Chap 1 Par 5 Page 5
wing skin is shown in Figure 1-8. Figure 1-9 shows internal corrosion of a tubular engine mount.
FIGURE 1-7. EXAMPLE OF BLISTERING OF SEALANT IN A FUEL CELL
CAUSED BY CORROSION FIGURE 1-8. EXAMPLE OF CHIPPED AND LOOSE PAINT ON A WING
SKIN CAUSED BY CORROSION Chap 1 Page 6 Par 5